\begin{tikzpicture}[scale=0.3]
    \begin{scope}
        \pgfmathsetmacro{\a}{8}
        \pgfmathsetmacro{\b}{6}
        \tkzDefPoints{0/0/A, \a/0/B, \a/\b/C, 0/\b/D}
        \tkzDrawPolygon(A,B,C,D)
        \tkzDrawSegments[dim={$\a$,-10pt,}](A,B)
        \tkzDrawSegments[dim={$\b$, 10pt,rotate=90}](A,D)
    \end{scope}

    \begin{scope}[xshift=11cm]
        \pgfmathsetmacro{\a}{8}
        \pgfmathsetmacro{\b}{4}
        \tkzDefPoints{0/0/A, \a/0/B, \a/\b/C, 0/\b/D}
        \tkzDrawPolygon(A,B,C,D)
        \tkzDrawSegments[dim={$\a$,-10pt,}](A,B)
        \tkzDrawSegments[dim={$\b$, 10pt,rotate=90}](A,D)
    \end{scope}

    \begin{scope}[xshift=22cm]
        \pgfmathsetmacro{\a}{6}
        \pgfmathsetmacro{\b}{4.5}
        \tkzDefPoints{0/0/A, \a/0/B, \a/\b/C, 0/\b/D}
        \tkzDrawPolygon(A,B,C,D)
        \tkzDrawSegments[dim={$\a$,-10pt,}](A,B)
        \tkzDrawSegments[dim={$\b$, 10pt,rotate=90}](A,D)
    \end{scope}
\end{tikzpicture}

